1. Field of the Invention
The present invention relates to improvement of a method of shutting off a conduit at joining flange portions of two pipes fastened and joined with each other with a fastener such as bolts, included in components together constituting a fluid piping system such as a waterworks piping system, for the purpose of e.g. replacement of a repair valve, a fire hydrant, an air valve, or the like which is disposed downstream of the joining flange portions. The invention relates also to improvement of a pipe conduit shutoff apparatus used in such method.
2. Description of the Related Art
A conventional pipe conduit shutoff apparatus includes a shutoff operation cover of a split construction attachable to the respective two pipe portions fastened and joined to each other by means of a fastener in such a manner as to seal the outer peripheries of the two joining flange portions, a gate plate valve in the form of a thin plate which can be inserted into a gap formed between the two joining flange portions in association with a loosening operation of the fastener to a position for shutting off the pipe conduit, and an operating means for switching over the gate plate valve, under the sealed condition, between a conduit shutting position and a conduit opening position.
The shutoff operation cover includes an annular elastic seal member to be pressed against the outer peripheral faces of the two joining flange portions, split fastener rings for fastening this annular elastic seal member from the radial outward direction, and a valve body accommodating case, wherein when the rear end of the gate plate valve comes into contact with the bottom inside the valve body accommodating case the leading end portion of the gate plate valve enters slightly an entrance side of a valve insertion hole defined in the annular elastic seal member or is located on the inner side of the valve body accommodating case than the entrance of the valve insertion hole (See Patent Documents 1, 2).
And, at the start of the attaching operation of the shutoff operation cover to the two pipe portions, to the annular elastic seal member in pressed contact with the outer peripheral faces of the two joining flange portions, the fastener rings are fitted and fastened thereon, with the rear end of the gate plate valve being placed in contact with the bottom inside the valve body accommodating case. After the outer peripheries of the two joining flange portions are surrounded with allowing a loosening operation of the fasteners, the gate plate valve is inserted through the valve insertion hole defined in the annular elastic seal member and the gap formed between the two joining flange portions in association with the loosening operation of the fastener up to a conduit shutting position, thereby to shut off the conduit between the two joining flange portions.    Patent Document 1: Japanese Patent Application “Kokai” No. 2006-144824    Patent Document 2: Japanese Utility Model Application “Kokai” No. 62-12090
With this type of pipe conduit shutoff apparatus, in association with a relative separating displacement of the two joining flange portions in response to a loosening operation of the fastener, relative movement along the pipe axis direction is allowed between the outer peripheral faces of the two joining flange portions and the annular elastic seal member of the shutoff operation cover. Therefore, when the shutoff operation cover is attached to the joining flange portions of the two pipe portions, there is the risk of the setting being made improperly, with the leading end portion of the gate plate valve of the shutoff operation cover being offset to one lateral side of the pipe axis direction from the annular gap formed on the outer peripheral sides of the opposing faces of the two joining flange portions.
However, even if the setting was done improperly with such offset as described above, this is hardly recognizable from the outside. Therefore, the gate plate valve placed under the conduit opening position tends to be moved to the conduit shutting position, with such improper attached condition un-corrected. As a result, the sharp leading end portion of the gate plate valve can hit the outer peripheral face of the joining flange portion, thereby deforming this portion.
The present invention has been made in view of the above-described state of the art and its principal object is to provide a method of shutting off a conduit and a pipe conduit shutoff apparatus capable of allowing efficient and easy attachment of the shutoff operation cover to the two joining flange portions at its proper attaching position and capable of restricting deformation of the leading end portion of the gate plate valve, through rational improvement utilizing the annular gap formed on the outer peripheral sides of the opposing faces of the two joining flange portions.